(Original post by TomX)
You want a flat stomach? The solution is not by doing situps (unless you did them for a long period of time, which then it would be class as cardiovascular activity), it's getting a proper diet and doing some sort of CV exercise (bikes, running, rowing, etc.). You've probably heard this all before 10^10 times but it's the only way (exception: liposuction).

Your lower back or neck may be hurting my doing situps if your back isn't strong enough to do situps, if it does hurt, seek another ab exercise (if you want strong abs that is) such as hanging hip raises.